Metallized film capacitors are used extensively in a broad range of electrical and electronic equipment that include motor run and motor start circuits for air conditioners, fluorescent and high intensity light ballasts, power supplies, telecommunication equipment, instrumentation, and medical electronics. In many of these applications, the metallized film capacitors (MFCs) are used to conserve energy by correcting the power factor of a circuit and in other applications they are used to perform specific functions, such as timing, filtering, and decoupling applications.
In order to reduce the dimensions of an MFC—an ever popular task—a thickness of a polymer film constituent of such capacitor should be reduced. The reduction of the thickness of the polymer film (such as, for example, a polypropylene film) is limited by the film-manufacturing process to a few microns. The related art (such as U.S. Pat. Nos. 6,165,832; 6,092,269; 5,731,948; 5,716,532; 5,097,800; 5,018,048 and 4,954,371) proposed some solutions to overcome this limitation by devising a new technological approach in which ultrathin vacuum-deposited polymer dielectrics are interleaved with vacuum-deposited metal electrode layers to form polymer monolithic capacitors with thousands of dielectric and electrode layers. During the fabrication, the dielectric materials are cross-linked with the use of electron beam or UV radiation. These capacitors are characterized by much higher energy density than conventional, polymer film capacitors.
Power electronics switching circuits (including inverter modules used in hybrid and electric vehicles, for example) utilize metallized film capacitors in the DC-link part of the circuit to minimize ripple current, voltage fluctuations, and to suppress transients. Key characteristics of DC-link capacitors used in voltage-sourced inverters of electric drive vehicles include self-healing properties to assure a benign failure mode, high ripple current capacity, low dissipation factor (DF), and high operating temperature. Metallized polypropylene film capacitors that service most DC-link applications are rated at 85° C. and can be used up to 105° C. with significant derating in voltage, ripple current and capacitor life. There remains a need in the industry to not only broaden the range of operating temperature of the MFCs and to extend the capacitor's upper operating temperature to at least 125° C. and preferably as high as 140° C., (while maintaining stable or substantially unchanged various operational characteristics such as, for example, capacitance and dissipation factor), but also to find ways to further reduce the capacitor's size and cost while maintaining a benign failure mode.